SiC2 in carbon stars: Merrill-Sanford absorption bands between 4100 and 5500 Å

Sarre, P. J.; Hurst, M. E.; Evans, T. Lloyd

doi:10.1046/j.1365-8711.2000.03818.x

Cited by 22 publications

(33 citation statements)

References 59 publications

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“…These molecular bands are identified between 4100−5500 Å in carbon stars (e.g. Sarre et al 2000;Yamashita & Utsumi 1968;and McKellar 1947). In fact we detect extra-absorptions around 4867 and 4906 Å, not present in the other stars of the sample, which coincides with the position of some band heads of this molecule.…”

Section: Analysis: the Extragalactic Carbon Stars And Their Chemical supporting

confidence: 63%

Chemical analysis of carbon stars in the Local Group

Laverny¹,

Abia

Domínguez

et al. 2006

A&A

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We present the first results of our ongoing chemical study of carbon stars in the Local Group of galaxies. We used spectra obtained with UVES at the 8.2 m Kueyen-VLT telescope and a new grid of spherical model atmospheres for cool carbon-rich stars which include polyatomic opacities, to perform a full chemical analysis of one carbon star, BMB-B 30, in the Small Magellanic Cloud (SMC) and two, IGI95-C1 and IGI95-C3, in the Sagittarius Dwarf Spheroidal (Sgr dSph) galaxy. Our main goal is to test the dependence on the stellar metallicity of the s-process nucleosynthesis and mixing mechanism occurring in AGB stars. For these three stars, we find important s-element enhancements with respect to the mean metallicity ([M/H]), namely [s/M] ≈ +1.0, similar to the figure found in galactic AGB stars of similar metallicity. The abundance ratios derived between elements belonging to the first and second s-process abundance peaks, corresponding to nuclei with a magic number of neutrons N = 50 (88Sr, 89Y, 90Zr) and N = 82 (138Ba, 139La, 140Ce, 141Pr), agree remarkably well with the theoretical predictions of low mass (M < 3 M ) metal-poor AGB nucleosynthesis models where the main source of neutrons is the 13 C(α, n) 16 O reaction activated during the long interpulse phase, in a small pocket located within the He-rich intershell. The derived C/O and 12 C/ 13 C ratios are, however, more difficult to reconcile with theoretical expectations. Possible explanations, like the extrinsic origin of the composition of these carbon stars or the operation of a non-standard mixing process during the AGB phase (such as the cool bottom process), are discussed on the basis of the collected observational constraints.

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Section: Analysis: the Extragalactic Carbon Stars And Their Chemical supporting

confidence: 63%

Chemical analysis of carbon stars in the Local Group

Laverny¹,

Abia

Domínguez

et al. 2006

A&A

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“…Many of the bands have double heads corresponding to ‘R’ and ‘Q’ rotational band structure, and in these cases we have two sets of the pairs of values for the wavelengths of the bandhead and of the peak emission intensity in Table 4. Agreement with the wavelengths of the same features measured on the absorption spectra of N stars (Sarre et al 2000) is better for the stronger features.…”

Section: Molecular Emission Features Of Iras 12311−3509mentioning

confidence: 51%

“…The star IRAS 12311−3509 is a most unusual object with an optical spectrum dominated by the Merrill–Sanford emission bands of SiC 2 . These bands are more commonly seen in absorption in cool N‐type carbon stars (see Sarre, Hurst & Lloyd Evans 2000). This star was discovered in a project aimed at identifying possible new RV Tauri stars selected from the IRAS Point Source Catalogue (Beichman et al 1988) on the basis of their characteristic colours in the [12]–[25], [25]–[60] diagram: they have red [12]–[25] and an excess at 60 μm relative to the majority of such stars (Lloyd Evans 1985; Raveendran 1989).…”

Section: Introductionmentioning

confidence: 99%

IRAS 12311−3509: a carbon star with SiC2 emission

Evans

Hurst

Sarre

2002

Monthly Notices of the Royal Astronomical Society

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The optical spectrum of the carbon star IRAS 12311−3509 is dominated by the Merrill–Sanford emission bands of SiC2, by absorption and emission in the Swan system of C2, and by resonance emission lines of neutral metals. The infrared energy distribution is flat from 1 to 60 μm. These observations are interpreted as arising from a star with a cool dusty disc which is edge‐on to the observer and obscures direct starlight. The infrared continuum is caused predominantly by absorption of stellar light by dust in the disc and re‐emission at longer wavelengths. The optical stellar spectrum is seen by reflection off dusty material which lies out of the plane of the disc, and the molecular and atomic emission arises in the same geometry through resonance fluorescence. The object has similarities to the J‐silicate stars, but may have a carbon‐rich rather than oxygen‐rich disc. A full spectroscopic assignment and discussion of the SiC2 bands and their intensities are given. Modelling of the rotational contours of the band yields a rotational temperature of 250 K, indicating very cool gas.

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“…The MS bands are sufficiently strong that they have been given their own index by Keenan (1993) in his revised classification scheme for carbon stars. More recently, a full assignment of the MS bands to individual vibrational transitions in the SiC 2 molecule has been given by Sarre, Hurst & Lloyd Evans (2000). These authors also provide a description of the historical development of the study of MS bands in astronomical and laboratory spectra.…”

Section: Introductionmentioning

confidence: 99%

“…MS bands are not seen in the majority of carbon stars, but when present they are usually quite strong, most probably because they are critically dependent on temperature – provided the star has sufficient carbon in its atmosphere (see Tsuji 1981; Barnbaum et al 1996). Barnbaum et al (1996) also noted that MS bands are most often observed in J‐type carbon stars; but this remark may be influenced by the fact that J‐type stars have more flux in the blue and consequently are more favourable for the study of MS bands (Sarre et al 2000).…”

Section: Introductionmentioning

confidence: 99%

Merrill-Sanford bands in Large Magellanic Cloud carbon stars

Morgan¹,

Hatzidimitriou²,

Cannon³

2004

Monthly Notices of the Royal Astronomical Society

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From a sample of 304 carbon stars in the central parts of the Large Magellanic Cloud (LMC), ∼27 per cent have Merrill–Sanford (MS) bands of the SiC2 molecule. The data are based on a uniform set of spectra taken with 2dF on the Anglo‐Australian Telescope, and give useful statistics on the incidence of MS bands and on their correlation (or otherwise) with other properties. All of these are red stars, cooler than 3100 K. The proportion of stars showing the bands is highest amongst the coolest stars, but not all very cool stars show the bands. There is no evidence that MS bands are more common in J‐type stars (carbon stars with a high 13C/12C ratio) than in N‐type carbon stars, at least within this sample of LMC stars. There is no apparent correlation with stellar variability, or between the photospheric temperature [as measured by (J−K)] and the occurrence of the ‘hot’ MS bands from excited molecular states.

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SiC2 in carbon stars: Merrill-Sanford absorption bands between 4100 and 5500 Å

Cited by 22 publications

References 59 publications

Chemical analysis of carbon stars in the Local Group

Chemical analysis of carbon stars in the Local Group

IRAS 12311−3509: a carbon star with SiC2 emission

Merrill-Sanford bands in Large Magellanic Cloud carbon stars

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